Chiral Octahedral Complexes of Cobalt(III) as “Organic Catalysts in Disguise” for the Asymmetric Addition of a Glycine Schiff Base Ester to Activated Olefins

Stereochemically inert and positively charged chiral complexes of cobalt(III) prepared from Schiff bases derived from chiral diamines and salicylaldehydes were shown to be efficient catalysts of the benchmark asymmetric phase‐transfer Michael addition of nine activated olefins to O’Donnell’s substrate. The reaction products had enantiomeric purities of up to 96%. DFT calculations were invoked to rationalize the stereochemistry of the addition.

     

Phosphorylation of Glycine Derivatives via Copper(I)‐Catalyzed Csp3−H Bond Functionalization

A simple and efficient one‐pot approach has been developed for a copper‐catalyzed phosphorylation of glycine derivatives under air and at room temperature. The present cross‐dehydrogenative coupling allows various methoxyphenyl‐protected glycine derivatives to be phosphorylated using diverse alkyl and aryl phosphites through an oxidative coupling between Csp³−H and P−H bonds catalyzed by copper iodide. This method provides a new synthetic tool to obtain biologically active α‐aminophosphonates.

     

Polymorphism and crystallization in poly(vinylidene fluoride)/ poly(ϵ‐caprolactone)–block–poly(dimethylsiloxane)–block–poly(ϵ‐caprolactone) blends

The miscibility, crystallization kinetics and crystalline morphology of a new system of poly(vinylidene fluoride)/poly(?‐caprolactone)‐block‐poly(dimethylsiloxane)‐block‐poly(?‐caprolactone) (PVDF/PCL‐b‐PDMS‐b‐PCL) triblock copolymer were investigated by a variety of techniques. The miscibility and phase behaviour of PVDF/PCL‐b‐PDMS‐b‐PCL were studied by determination of the melting point temperature, crystallization kinetics and Fourier transform infrared (FTIR) mapping. Chemical imaging was used as a new technique to characterize the interaction of polymer blends in crystalline morphology. The results demonstrate the existence of characteristic peaks of both PVDF and PCL in the chosen crystalline area. The crystalline structures of PVDF were affected by the PCL‐b‐PDMS‐b‐PCL triblock copolymer and facilitate the formation of the β polymorph which was illustrated by FTIR analysis. The β crystal phase fraction increases significantly on increasing the composition of the PCL‐b‐PDMS‐b‐PCL triblock copolymer. In addition, confined crystallization of PCL within PVDF inter‐lamellar and/or inter‐fibrillar regions was confirmed through polarizing optical microscopy, wide‐angle X‐ray diffraction and small‐angle X‐ray scattering analysis. © 2019 Society of Chemical Industry     

Cobalt(II)‐Catalyzed Electrophilic Alkynylation of 1,3‐Dicarbonyl Compounds To Form Polysubstituted Furans via π–π Activation

Polysubstituted furans were obtained with excellent yields via the electrophilic alkynylation of 1,3‐dicarbonyl compoundsws with phenyl‐ or ester‐substituted brominated alkynes. The reaction is catalyzed by the inexpensive and readily available catalyst, cobalt(II) chloride, and has a wide substrate scope. The C(sp) C(sp³) coupling occurs under mild conditions with short reaction times and does not require an inert atmosphere or ligands. It is proposed that the reaction proceeds through a chelation complex of cobalt(II) with the deprotonated 1,3‐dicarbonyl compound.

     

The specific volume of poly(tetrafluoroethylene) as a function of temperature (30°–372°C) and pressure (0–2000 kg/cm2)

Experimental data on the specific volume of a 50% crystalline sample of poly(tetrafluorethylene) are presented and discussed. Data points were taken along 22 isotherms spaced 5 to 30°C apart (up to 372°C) in pressure increments of 100 kg/cm² up to 2000 kg/cm². In addition to the melting transition and the first-order solid–solid transition near room temperature, a previously reported second-order transition near 140°C at P = 0 is observed. This transition shifts to higher temperatures with increasing pressure by about 0.015°C per kg/cm². The melt data are discussed in detail. They can be fitted to both the empirical Tait equation, with the usual exponential temperature dependence of the Tait parameter, and to the Simha-Somcynsky hole theory (with the reducing parameters V^* = 0.424 cm³/g, T^* = 7906°K, and P^* = 7100 kg/cm² = 6960 bars), thus providing a test for this theory at high reduced temperatures near T? = 0.08.     

Chemical Synthesis of the Epimeric (23R)‐ and (23S)‐Fluoro Derivatives of Bile Acids via Horner–Wadsworth–Emmons Reaction

A method for the synthesis of two (23R)‐ and (23S)‐epimeric pairs of 23‐fluoro‐3α,7α,12α‐trihydroxy‐5β‐cholan‐24‐oic acid and 23‐fluoro‐3α,7α‐dihydroxy‐5β‐cholan‐24‐oic acid is described. The key intermediates, 23,24‐dinor‐22‐aldehyde peracetates were prepared from cholic and chenodeoxycholic acids via the 24‐nor‐22‐ene, 24‐nor‐22ξ,23‐epoxy, and 23,24‐dinor‐22‐aldehyde derivatives. The Horner–Wadsworth–Emmons reaction of the 23,24‐dinor‐22‐aldehydes using triethyl 2‐fluoro‐2‐phosphonoacetate in the presence of LiCl and 1,8‐diazabicyclo[5,4,0]undec‐7‐ene (DBU), and subsequent hydrogenation of the resulting 23ξ‐fluoro‐22‐ene ethyl esters, followed by hydrolysis, gave a mixture of the epimeric (23R)‐ and (23S)‐fluorinated bile acids which were resolved efficiently by preparative RP‐HPLC. The stereochemical configuration of the fluorine atom at C‐23 in the newly synthesized compounds was confirmed directly by the X‐ray crystallographic data. The ¹H and ¹³C NMR spectral differences between the (23R)‐ and (23S)‐epimers were also discussed.     

Evaluation of a 7‐Methoxycoumarin‐3‐carboxylic Acid Ester Derivative as a Fluorescent,Cell‐Cleavable,Phosphonate Protecting Group

Cell‐cleavable protecting groups often enhance cellular delivery of species that are charged at physiological pH. Although several phosphonate protecting groups have achieved clinical success, it remains difficult to use these prodrugs in live cells to clarify biological mechanisms. Here, we present a strategy that uses a 7‐methoxycoumarin‐3‐carboxylic acid ester as a fluorescent protecting group. This strategy was applied to synthesis of an (E)‐4‐hydroxy‐3‐methyl‐but‐2‐enyl diphosphate (HMBPP) analogue to assess cellular uptake and human Vγ9Vδ2 T cell activation. The fluorescent ester displayed low cellular toxicity (IC₅₀>100 μm ) and strong T cell activation (EC₅₀=0.018 μm ) relative to the unprotected anion (EC₅₀=23 μm ). The coumarin‐derived analogue allowed no‐wash analysis of biological deprotection, which revealed rapid internalization of the prodrug. These results demonstrate that fluorescent groups can be applied both as functional drug delivery tools and useful biological probes of drug uptake.     

Direct Enantioselective Three‐Component Kabachnik–Fields Reaction Catalyzed by Chiral Bis(imidazoline)‐Zinc(II) Catalysts

A direct three‐component reaction of aldehydes, amines and diaryl phosphites was catalyzed by a zinc(II) complex of 1,3‐bis(imidazolin‐2‐ly)pyridine (pybim) giving the corresponding α‐aminophosphonates in good yield with good enantioselectivity. The reaction was applied to a wide variety of aromatic aldehydes to give products with excellent yields (up to 99%) and enantiomeric excesses (up to 93% ee).     

4–Hydroxy–3–arylamino–l, 8–naphthalimides and 3–(and 4–) hydroxy–2–(and 5–) arylamino–7H–bcnzimidazo–(2, l–a)benz(d,e)isoquinolin–7–ones. Red dyes for synthetic–polymer fibres

4–Hydroxy–1, 8–naphthalimides and the isomer mixtures of'3–and 4–hydroxy–7 H–benzimidazo–(2, l–a)–benz(d, e)–isoquinolin–7–ones were coupled with diazotised arylamines to yield orange–red to bluish–red dyes having good coloration properties and excellent fastness to light on polyester fibres. Structure–property relationships in the dyes are discussed with respect to the nature of the substituents in the imide, imidazole and arylazo moieties.     

The specific volume of poly(4-methylpentene-1) as a function of temperature (30°–320°C) and pressure (0–2000 kg/cm2)

The dependence of the specific volume of a commercial sample of poly(4-methylpentene-1) (Mitsui TPX, RT-20, abbr. PMP) on temperature (30°–320°C) and pressure (0–2000 kg/cm²) has been determined. Results are reported in tabular form and as approximate fits, making use of the Tait equation. The data show that the crystalline melting transition of this type of PMP is completed at 235°C under zero pressure and gives indication of a glass transition temperature T_g at about 20°C at p = 0. Its approximate pressure dependence is given by dT_g/dp ≈ 0.015°C kg^?1 cm². The zero pressure results on the melting and glass transitions are in agreement with DTA results. The p-v-T data, quenching experiments, and a determination of the crystalline unit cell (tetragonal, a = b = 18.70 Å, c = 13.54 Å) confirm earlier work indicating that the room-temperature crystalline specific volume of PMP is greater than the amorphous specific volume. This unusual density behavior persists to a temperature of 50–60°C at p = 0 and to temperatures as high as 230–240°C under a pressure of 2000 kg/cm².     

Highly Enantioselective Hydrogenation of Itaconic Acid Derivatives with a Chiral Bisphospholane‐Rh(I) Catalyst

The new – commercially in multi‐kg quantities available – chiral bisphospholane ligand, catASium^® M, has been successfully used in the Rh(I)‐catalysed enantioselective hydrogenation of itaconic acid derivatives. Chiral ß‐substituted succinic acid derivatives were produced in good to excellent enantioselectivities. Turnover frequencies by up to 40,000 h⁻¹ have been achieved.     

Chiral Amino Diol Derivatives as New Modular Organocatalysts for the Enantioselective α‐Chlorination of Cyclic β‐Keto Esters

Highly modular chiral amino diol derivatives have been used as organocatalysts in the enantioselective α‐chlorination of cyclic β‐keto esters. Optimization of the catalyst structure and the reaction conditions has allowed the synthesis of optically active α‐chlorinated products with high enantioselectivities (up to 96% ee) using inexpensive commercially available N‐chlorosuccinimide (NCS) as the chlorine source under mild conditions.     

Frying as a science – An introduction

Frying is an ancient process, but it is only in the past fifty years that it has gained the attention it deserves from the scientific community. Early frying research tended to focus almost exclusively on the chemistry of the frying oil. Some of the pioneering work is summarized. Recent work has been looking at frying as a system, that is, the oil, the food, the fryer and the operation in general. This approach has yielded greater understanding of the process and has already led to improvements in frying operations. New ideas and aims are presented and these may lead to and create a framework for future work in deep‐fat frying.     

The tert.-Butyloxycarbonyl-(Boc) Group,a Suitable 2′-OH-Protecting Group in Oligoribonucleotide Solid-Phase Synthesis

The solid-phase synthesis of the dodecaribonucleotide ACCACUAAAGCG is described using the tert. butyloxycarbonyl (Boc) as 2′-OH-protecting group. The synthesis was carried out on a filter disc support Whatman 3 MM by the phosphotriester method. Under these conditions, the 2′-OH-Boc-group proved to be absolutely stable. Moreover, it is quantitatively and selectively removable by 4n HCl/dioxane. Thus, the group renders to be an excellent persistent 2′-OH-protection in ribonucleotide synthesis.     

Porous poly(ethylene glycol)–polyurethane hydrogels as potential biomaterials

We report the synthesis of porous poly(ethylene glycol)–polyurethane (PEG‐PU) hydrogels using PEG‐4000 as a soft segment and 4,4′‐methylenebis(cyclohexylisocyanate) as a hard segment. The degree of swelling in the hydrogels could be controlled by varying the amount of crosslinking agent, namely 1,2,6‐hexanetriol. Structural characterization of the hydrogels was performed using solid‐state ¹³C NMR and Fourier transform infrared spectroscopy. Wide‐angle X‐ray diffraction studies revealed the existence of crystalline domains of PEG and small‐angle X‐ray scattering studies showed the presence of lamellar microstructures. For generating a porous structure in the hydrogels, cryogenic treatment with lyophilization was used. Scanning electron microscopy and three‐dimensional micro‐computed tomography imaging of the hydrogels indicated the presence of interconnected pores. The mechanical strength of the hydrogels and xerogels was measured using dynamic mechanical analysis. The observed dynamic storage moduli (E′) for the equilibrium swollen and dry gels were found to be 0.15 and 4.2 MPa, respectively. Interestingly, the porous PEG‐PU xerogel also showed E′ of 5.6 MPa indicating a similar mechanical strength upon incorporating porosity into the gel matrix. Finally, preliminary cytocompatibility studies showed the ability of cells to proliferate in the hydrogels. These gels show promise for applications as scaffolds and implants in tissue engineering. © 2014 Society of Chemical Industry     

Preparation and properties of poly(benzyl glutamate)–poloxamer–poly(benzyl glutamate) and poly(glutamic acid)–poloxamer–poly(glutamic acid) triblock polymers

The novel block copolymer poly(benzyl glutamate) (PBLG)–polomamer–PBLG were synthesized from glutamic acid and poloxamer in six steps with three different molecular weights, and another new block copolymer, poly(glutamic acid) (PGA)–poloxamer–PGA, was obtained by the benzyl deprotection of PBLG–poloxamer–PBLG. The obtained compounds were characterized by IR spectroscopy, gel permeation chromatography, and ¹H‐NMR. The in vitro biological degradation and water absorption of PBLG showed that a greater proportion of PBLG in the copolymer led to a slower degradation and weaker water absorption, so the speed of degradation and water absorption could be adjusted through adjustment of the ratio of poloxamer. Both PBLG–poloxamer–PBLG and PGA–poloxamer–PGA exhibited lower cytotoxicity and good biocompatibility in the methyl thiazolyl tetrazolium (MTT) assay. The results show that both block polymers are promising as drug‐carrier materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The Synthesis and Ultraviolet Spectra of Nitrodiphenylamine Disperse Dyes I–Derivatives of 2, 4– and 2, 6–Dinitrodiphenylamine

Condensation of l–chloro–2, 4– and –2, 6–dinitrobenzene with arylamines readily affords the corresponding dinitrodiphenylamines.